“Matchmaker” protein essential for bringing plants and fungi together in symbiotic relationship

Lifelong symbiotic relationships between plants and fungi are set up thanks to a protein that enables them to “communicate” researchers have found. The study shows that the transporter protein, which was previously unidentified in plants, conditions fungi to establish a mutually beneficial relationship with the plant.

Plants such as maize and rice are able to establish a mutually beneficial relationship with fungi through a protein which enables them to “communicate”, and ultimately find, each other, a new study has found.

The interrelationship between the two enhances the ability of both species to take up vital nutrients, such as phosphate from the soil. The new research, led by Dr Uta Paszkowski, a Fellow of St John’s College, University of Cambridge, has shown that the early formation of this relationship depends on the presence of a newly-identified transporter protein.

This symbiosis (the term for a mutually advantageous relationship between two organisms) can profoundly influence plant performance in both wild and cultivated settings. Understanding more about the process could help scientists to develop sustainable means of producing more food for the world’s growing population.

The researchers studied the association between plants and the arbuscular mycorrhizal (AM) fungus.  Through this fungus, the plants increase the surface area of their roots, significantly extending their reach. The fungus establishes itself within the plant roots and grows long, branching extensions underground called hyphae which facilitate the uptake of minerals from the soil. Simultaneously, the fungus obtains the nutrients it needs to survive from the plant.

“The fungus and the plant need each other as symbiotic partners, and communication is vital in finding each other,” Paszkowski, the study’s principal investigator, said. “Wild type plants release something that conditions the fungus for symbiosis, but if the plant can’t talk to the fungus, the fungus won’t be able to respond.”

Until now, little has been known about how this process happens. Most research has focused on the stimulatory role of plant hormones called strigolactones, which influence fungal metabolism and development.

The new study, however, analysed a mutant strain of maize that does not form symbiotic associations with fungi at all. By examining this, the researchers were able to identify a missing gene, absent from the mutant maize called NOPE1. This codes for a previously unknown transporter molecule which, in turn, allows for the uptake and release of a protein called N-acetylglucosamine (GlcNAc) – a fibrous substance which is a major component of the cell walls of most fungi and also of many signalling molecules.

“The GlcNAc transporter molecule is the first plant protein ever reported to be indispensable for communication between plants and the fungus in the rhizosphere – the region of soil accessible to both fungus and plant root,” Paszkowski said.

The study, published in Nature Plants, suggests that the NOPE1 gene must be working properly if AM fungi in the soil are to respond to the signals released by plant roots, and thus begin the process of forming a symbiotic relationship between the two. Previous research has already shown that once GlcNAc is transported into a fungal cell, it activates cell signalling and increases the expression of genes needed to promote interactions with the host plant.

The researchers confirmed this by exposing AM fungi to secretions from rice plant roots with functioning NOPE1. As expected, this caused the fungi to invade the roots of plants, and to express genes that help them attach to host plant cells.

Managing this process to naturally fertilise crops is, they suggest, one potential approach to help feed the world’s growing population sustainably – and an alternative to chemical fertilisers which are expensive and damaging to the environment. The research adds to a growing body of evidence which indicates that it is now possible to develop new strains of crop that work better in low-input agricultural systems. Smallholder farmers in poorer count tries could better afford these, leading to improved crop yields and more income.

“By better understanding this early communication process we can find ways to manage the establishment of symbiosis, for example to achieve a faster delivery of nutrients to crops from the soil,” Paszkowski added. “In crops with a short growing season, speeding up symbiosis development could reduce the amount of phosphate fertiliser needed. It would be a cheaper and more sustainable way of growing crops.”

An N-acetylglucosamine transporter required for arbuscular mycorrhizal symbioses in rice and maize is published in Nature Plants and available in full via: https://www.nature.com/articles/nplants201773.